Silicon hydride surface intermediates for chemical separations apparatus

ABSTRACT

The present invention produces very stable, covalently bonded separation substrates for separations application such as liquid and gas chromatography as well as capillary zone electrophoresis. An intermediate substrate is prepared which has hydride species on the substrate surface. These hydrides preferably are further derivatized by the catalytic addition of organic compounds bearing a terminal vinyl group. The final surface modification contains closely packed, direct carbon linkages that are stable.

FIELD OF THE INVENTION

This invention relates to a surface-modified material used in a varietyof separation applications, such as chromatography or electrophoresis.

More particularly, the invention pertains to a chemically modifiedmineral oxide, such as silica or quartz, which exhibits improvedhydrolytic stability, larger organic coverage and superior separativecapabilities when formed into various forms or shapes, such as porousbeads or capillary tubes.

BACKGROUND OF THE INVENTION

Chemically modified silicas have been, and continue to be, widely usedas supports in a great variety of chromatographic separations. With theaim of controlling its selectivity while reducing unwanted interactionswith one or more compounds, numerous synthetic procedures have beendeveloped to attach organic moieties (R) on the silica surface. Earlywork on the chemical modification of silica described the use of anesterification reaction between surface silanol groups and an alcohol togive Si-O-C linkages (Halasz and Sebastian, Angew. Chem. (Int. Ed.)8:453 (1969); Deuel, et al., HeIv. Chim. Acta 119:1160 (1959)). Althoughsuch materials were useful for many separations, their limitedhydrolytic stability seriously precluded the extensive usage of thesebonded phases, particularly in liquid chromatography which requires theuse of aqueous eluents.

Currently, commercially available bonded phases are prepared by reactingselected organosilanes with the silica surface. Halogen- oralkoxy-substituted alkyldimethylsilanes react with the surface silanolsattached to the silica surface through an Si-0-Si-C linkage. By usingthis approach it is possible to produce bonded silicas with a greatvariety of organic groups, ranging from non-polar materials, forinstance, octyl- and octadecyl-silicas (R --(CH₂)_(n) CH₃, with n-7 and17 respectively) commonly used as bonded supports in reversed-phaseliquid chromatography, to ionic materials such as benzenesulphonic acidderivatives, which are widely used in ion-exchange liquidchromatography. The preparation of these and similar materials aredescribed in a number of publications (e.g., Roumeliotis and Unger, J.Chromatogr. 149:211 (1978) or Asmus, et al., J. Chromatogr. 123:109(1976)) and patents (Sebastian, et al., U.S. Pat. No. 3,956,179; Hancok,et al., U.S. Pat. No. 4,257,916; or Ramsden, et al., U.S. Pat. No.4,661,248).

The new development of electrophoretic separations in a capillary formathas promoted the extent of the silane technology normally used inchromatography to the deactivation of the inner wall of the quartzcapillary. Thus, Jorgenson, et al. (Science 222:266 (1983)) have notedthat separation of model proteins, such as cytochrome, lysozyme andribonuclease A, in untreated fused silica capillaries with a phosphatebuffer at pH 7 was accompanied by strong tailing, and suggested thatthis might be caused by strong interactions of the proteins and thecapillary wall. Derivatization of the capillary wall has been proveneffective to prevent or control protein sorption. In another application(U.S. Pat. No. 4,680,201 issued 1987), Hjerten describes a method forpreparing a thinwall, capillary tube for electrophoretic separations byuse of a bifunctional compound in which one group (usually a terminal--SiX₃ group where X=Ethoxy, methoxy or chloride) reacts with the glasswall and the other (usually an olefin group) does so with a monomertaking part in a polymerization process. This process resulted in awall-bonded, polymer-filled capillary useful for polyacrylamide gelelectrophoresis. In addition, by chemically modifying the quartz surfaceof the capillary, operational variables such as the electroosmotic floware said to be more amenable to control.

The extensive usage of these bonded materials in chromatography andcapillary electrophoresis does not necessarily imply that they meet allrequirements with respect to separation performance and stability. Onthe contrary, they are subject to serious effects arising primarily froma relatively limited organic coverage due to the "bulky" methyl groupsof the silane reagent and from a still unsatisfactory hydrolyticstability, particularly under moderately acidic or slightly alkalineelution conditions. This limited surface coverage along with ahydrolytically labile organic layer both result in the exposure of asubstantial number of surface silanols, groups which are known to beprimarily responsible for the residual adsorption phenomena that plaguesilicon-based materials. These so called "silanophilic" interactions areusually undesirable in chromatography as well as in capillaryelectrophoresis because they often result in "tailing" peaks, catalyzedsolute decomposition, lead to unreliable quantitation, etc. One of themost striking cases of silanophilic interactions occurs perhaps in theseparation of certain compounds containing amino or other similargroups, particularly biomolecules. For instance, many proteins mayinteract very strongly with unreacted silanols leading to excessive bandtailing, incomplete recovery of one or more solutes, or even recovery ofthe same component from different bands. As a result of such problems,other organosilane reagents have been developed.

Two related approaches have been proposed in which the methyl groups ofthe organosilane reagent are replaced either by a "bidentate" or by abulkier group (Kirkland and McCormick, Chromatographia 24:58 (1987)). Inboth cases the new groups are aimed to shield the unreacted silanols aswell as the hydrolytically labile linkage that bonds the silane to thesupport. Although this steric protection has resulted in somewhatimproved bonded phases, the necessity still exists for a truly effectivesilane chemistry.

In another completely different approach, bonded silicas bearing directSi-C linkages have been developed. They involve the sequential reactionof the silica substrate with a chlorinating reagent (e.g., thionylchloride) and a proper alkylating reagent (e.g., a Grignard ororganolithium compound). In principle this method should provide notonly a closer attachment and a denser coverage of organicfunctionalities but also a more hydrolytically stable bonded phase thanthat obtained by the corresponding Si-O-Si-C linkage. Nevertheless, theapplication of chlorination/Grignard or chlorination/organolithiumreaction sequence to modify silica substrates has been hindered byseveral factors. One factor is that the one-step organosilanization(such as described in U.S. Pat. No. 3,956,179 to Sebastian, et al.) isrelatively easy to produce materials as compared to the two-stephalogenation/alkylation which, additionally, demands rigorousmoisture-free conditions. Difficulties associated with the removal ofresidual salts which may be occluded in the porous silica matrix duringthe alkylation process is also an important factor which has contributedto the limited usage of this synthetic approach. Additionally, thepreparation of the alkylation reagent exhibits strong interferences withmany reactive functionalities, particularly those containing carbonyl,nitrile, carboxyl, amide, alcohol, etc. That is, the great reactivitywhich makes a Grignard reagent so useful in many synthetic approachesseriously limits its applicability. The organic group, R, in theGrignard reagent, RMgBr, must remain intact during the preparation ofthe reagent. It is a well known fact that Grignard reagents react withacidic components to form the corresponding hydrocarbon group R-H. Morestrictly, "any compound containing hydrogen attached to anelectronegative element such as oxygen, nitrogen, and even triply-bondedcarbon are acidic enough to decompose a Grignard reagent" (Morrison andBoyd, Organic Chemistry, 3rd Edition, 1974). Additionally, a Grignardreagent reacts readily with molecular oxygen, carbon dioxide, and with "nearly every organic compound containing a carbon-oxygen or carbon

nitrogen multiple bond" (supra). The group nitro (--NO₂) also appears toreact oxidatively with a Grignard reagent. It seems clear therefore thatonly a very limited number of organic functionalities may be present inthe halide compound from which a Grignard reagent can be prepared. Beingeven more reactive than the corresponding Grignard reagent, anorganolithium reagent should exhibit the same limitations describedabove in a similar or greater extent. This, of course, greatly limitsthe versatility of this approach.

It is therefore desirable to address the shortcomings of existing bondedpackings by developing an alternate silane chemistry which combines thesuperior coverage and hydrolytic stability of direct Si-C linkages withthe preparation simplicity of silane derivatization.

SUMMARY OF THE INVENTION

In one aspect of the invention, a surfacemodified material is producedcomprising an inorganic oxide substrate (such as silica, quartz oralumina). The surface of this material, or substrate, has beenchemically modified. The chemical modification is whereby hydridespecies are formed. These hydride species can then be further reacted.When further reacted, the substrate surface is thus chemically modifiedso as to bear a variety of functionalities covalently attached to thesupport, through hydrolytically stable surface-to-carbon linkages.

In another aspect of the invention, a method for modifying the surfaceof an inorganic oxide substrate is provided, comprising two major steps:(1) attachment of hydride species on the substrate so as to give arelatively stable intermediate; and (2) reacting said hydrided surfacewith organic compounds bearing a terminal vinyl group, in the presenceof a catalyst, whereby direct linkage of said inorganic substrate tocarbon is provided.

It is a primary purpose of this invention to provide a surface-modifiedseparation material which exhibits extended lifetime (hydrolyticallystable), displays improved adsorption properties (larger and moreversatile organic coverage), and is substantially free of contaminants(e.g., residual salts and the like).

The method of making this surface-modified material is a very versatilein that it provides an effective means of attaching organicfunctionalities to an inorganic substrate which otherwise cannot beintroduced by regular organometallic procedures. Thus, the presentinvention provides a method suitable to prepare bonded substrates havingdirect carbon-substrate linkages whose organic part includesfunctionalities that otherwise could not be present in the organic partof Grignard or organolithium reagents. Thus, compounds having a hydrogenattached to oxygen, nitrogen and to a triply-bonded carbon, compoundscontaining a carbonoxygen and carbon-nitrogen multiple bond, andcompounds containing a nitro group can be used to modify substrates inaccordance with the invention, where such compounds would be foreclosedwere Grignard and organolithium reagents to be utilized in the method.

The present invention represents a totally different approach to theprior problems in producing very stable, covalently bonded separationsubstrates for all types of liquid and gas chromatography as well ascapillary electrophoresis. The new procedure involves the preparation ofan intermediate which provides silicon hydride species on the silicasurface, followed by the catalytic addition of such silicon hydrides toorganic compounds bearing a terminal vinyl group. The final productcontains closely packed direct Si-carbon linkages, thus providing asignificantly improved surface-modified separation substrate with regardto stability and silanophilic interactions. Additionally, because of theintrinsic freedom from interferences of the catalytic SiH addition (alsoknown as hydrosilation or hydrosilylation), the method of preparation isan extremely versatile one in that it allows bonding of virtually anyorganic functionality to a support material, in a clean, high-yieldprocedure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a partial IR spectrum of a hydride intermediateembodiment;

FIG. 2 illustrates a partial IR spectrum of another hydride intermediateembodiment;

FIG. 3 illustrates a partial IR spectrum of an octyl-bonded silicaembodiment; and

FIG. 4 illustrates a partial IR spectrum of an octadecyl-bonded silicaembodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This invention differs from most of the methods currently available byusing a direct substrate-to-carbon bond instead of a substrate-O-Si-Ctype of linkage. This invention describes a unique process whichinvolves the catalytic addition of surface hydride species to an organicreagent containing a double bond, after converting the original surfacehydroxyl to hydride groups. By contrast to other procedures, thisinvention requires neither additional post-reaction (end-capping)treatment, nor extensive clean-up procedures.

In one preferred embodiment, the substrate material to be modifiedaccording to the method described herein is silicon oxide in the form ofsilica, quartz or the like materials. These oxides are commonly used ingas and liquid chromatographic, as well as in capillary electrophoretic,separations. Alternative suitable substrates include other inorganicoxides, such as alumina, thoria, magnesia and combinations thereof. In aparticularly preferred embodiment, the substrates to be modified areporous, particulate silica (such as beads) as well as non-porous quartzcapillary tubes.

The modification method of the present invention comprises two majorsteps. One of the inorganic oxides as described above is provided; sucha material provides a surface bearing hydroxyl groups. These hydroxylgroups provide active sites which can be chemically transformed intohydride groups. This is accomplished either by direct conversion of thehydroxyl groups to hydride groups (via a chlorination/reductionsequence) or by condensation of the surface hydroxyl groups with ahydridosilane coupling reagent. In either case, a chemically andthermally stable hydrided intermediate is obtained in which most of theoriginal hydroxyl groups are replaced by silicon hydride species. In thesecond major step, the hydrided surface is reacted with an organiccompound containing a double bond, preferentially a terminal vinylgroup, in the presence of an appropriate catalyst so as to give a directlinkage of the surface to carbon.

One procedure to prepare the hydride intermediate material via thehalogenation/reduction sequence is as follows. A predetermined quantityof inorganic oxide substrate, e.g., silica, is added to an anhydroussolvent such as toluene and a suitable excess of a halogenating reagentis added thereto, preferably thionyl chloride. The reaction is allowedto proceed under a nitrogen atmosphere at reflux for 18-24 hours, atwhich point the halogenated solid is isolated, washed and dried.Reduction is effected by slowly adding the halogenated material to asuitable excess of an ethereal solution of an inorganic hydride such aslithium aluminum hydride. The reaction is carried out in a reactorequipped with a condenser containing a suitable frigorific mixture sucha dry ice/acetone. The reduction is allowed to proceed at roomtemperature for about 3-5 hours, under nitrogen atmosphere. The reducedmaterial is finally subjected to a "clean-up" step so as to removecontaminating salts (e.g., aluminum chloride) from the reducing reagent.The solid is washed several times with diluted aqueous acid, after whichthe product is rinsed with water and a suitable alcohol such asmethanol. The solid then dried at high temperature for several hours,typically at 110° C. overnight (see Example 1).

One alternate procedure to prepare the hydride intermediate is asfollows: A predetermined quantity of inorganic oxide substrate, e.g.,silica, is added to a dilute alcoholic mineral acid solution (typicallya 0.1M HCl solution in 95% ethanol) and a suitable excess of ahydridosilane agent is added thereto, preferably a trialkoxysilane ortrihalosilane such as triethoxysilane or trichlorosilane. The reactionis allowed to proceed for several hours (typically 2-6 hours), at whichpoint the hydrided material is isolated and washed with alcohol (seeExample 5).

Catalytic hydrosilation of olefins on the hydrided substrate is carriedout as follows. A predetermined quantity of hydride intermediateprepared as described above is added to a suitable excess of solution ofthe olefin in a preferably anhydrous solvent such as toluene orchloroform. No solvent is usually required with liquid olefins. Theolefin solution also contains an amount of catalyst complex so that anapproximate 1:10⁴ molar ratio of catalyst to hydride is attained. Thereaction is allowed to proceed for 18-24 hours at elevated temperature,typically 80-100° C., at which point the bonded material is isolated andwashed (see Examples 6 and 7). Depending upon the desired product, theolefin reagent is selected from a large number of organic compounds,preferably those bearing a terminal vinyl group, i.e., those with thegeneral formula CH₂ =CH-R where R ranges from simple hydrocarbon groupssuch as n-alkyls, to heteroatom compounds such as carbonyls, nitriles,amides, etc.

Because of easy availability, chloroplatinic acid is the preferredcatalyst used, usually in a 2-propanol solution. However, othertransition metal complexes can be used with similar results.

Thus, the present invention provides a surfacemodified materialcomprising an inorganic oxide that originally had surface hydroxylgroups. These surface hydroxyl groups are chemically modified so as toprovide a covalently bonded organic layer having a plurality offunctionalities. Among the functionalities that may be present in thecovalently bonded organic layer (where the bonding is by means of adirect carbon-substrate linkage) are where a hydrogen is attached tooxygen, nitrogen and to a triply-bonded carbon, where there is acarbon-oxygen and carbon-nitrogen multiple bond, and where there is oneor more nitro groups. The inorganic oxide material preferably isselected from oxides of silicon, aluminum, zirconium, tin, titanium, andcombinations thereof. Suitable substrates include quartz and particulatesilica.

Where silica is selected, then the silica may be porous (such as acolumn packing material suitable for gas and liquid chromatography) ornon-porous (such as a non-porous capillary tube). Porous silicaspreferably have a surface area of at least about 100 m² /g and anaverage pore diameter of about 60 Å, although surface areas can be inthe range of about 50 to a few hundred m² /g and pore diameters canrange from 30 to about 500 Å. Non-porous capillary tubes typically havean inner diameter less than about 500 μ, more typically between about 20μto about 200 μ.

Whether porous or non-porous, the inorganic oxide substrates arepreferably rigid and noncollapsible structures since, for example,column packing materials often must withstand pressures that can be onthe order of several thousand psi and capillary tubes require structuralintegrity.

In accordance with the invention, the surface hydroxyl groups initiallypresent on the inorganic oxide substrate are reacted so as to give anintermediate material containing surface hydride groups. This reactingstep may be performed by either one of two procedures. One procedure isa halogenation/reduction sequence. The other procedure is a singlesilane coupling reaction. The halogenation/reduction sequence compriseshalogenation of the inorganic oxide substrate followed by reduction ofthe halogenated material and preferably by post-reaction treatment withaqueous acid. Such halogenation is preferably accomplished with achlorinating reagent. A particularly preferred chlorinating reagent isthionyl chloride, although other suitable chlorinating reagents includebut are not limited to SiCl₄, S₂ Cl₂, Cl₂ CO, CCl₄ and CH₃ COCl. Thehalogenated material, or moieties, are then reacted with an inorganichydride. Suitable inorganic hydrides include aluminum hydrides, boronhydrides, and the like.

If a single silane coupling reaction is selected as the procedure inaccordance with the invention, then the coupling reagent preferably is ahydridosilane of the formula H_(n) SiX_(4-n) where X is a hydrolyzablegroup, and n is an integer in the range of 1 and 3. Particularlypreferred such hydride silane coupling reagents are triethoxysilane andtrichlorosilane.

These solid intermediates so obtained are then further derivatized. Thefurther derivatization is preferably by reacting the intermediatehydrides with an olefin reagent in the presence of a catalyst wherebydirect linkage to carbon is obtained.

As previously known in other contexts, the addition of silicon hydridesto alkenes is one of the most important laboratory methods to form Si-Cbonds. The reaction's minimal interferences with other reactivefunctionalities (e.g., CO₂ R, NH₂, etc.) has permitted the attachment ofsilicon to organic molecules which otherwise cannot be introduced byregular organometallic procedures. Hydrosilation is generally carriedout in the presence of a transition metal catalyst. A variety ofinorganic and organic complexes of platinum, rhodium, palladium,ruthenium, iridium and nickel have functioned as very effectivecatalysts for the addition reaction. Chloroplatinic acid in anisopropanol solution (also known as "Speiers" catalyst) is the mostcommonly used form. Only as little as 10⁻³¹ 5 mole of platinum per molof silicon hydride is normally required for an effective hydrosilation.The addition is rapid and can be done at room temperature or underreflux to ensure a high yield. Details of the reaction in homogeneousphase can be found elsewhere (e.g., Speier, Adv. Organomet. Chem 17:407(1979); Seyferth, editor, J. Organomet. Chem. Library 5:1 (1977)).

Among the advantages of practice of the invention are that therelatively limited organic coverage due to the "bulky" methyl groups ofprior art organosilanes can be avoided and more hydrolytically stablesurface modifications may be obtained. Additionally, the advantages ofdirect Si-C linkages may be achieved without the disadvantages thatoccur when obtained by the known sequential reaction with chlorinatingreagent and an alkylating reagent such as Grignard. Thus, the presentinvention not only combines the superior coverage and hydrolyticstability of direct Si-C linkages with a simplicity approaching that ofsilane derivatization, but also dramatically increases the versatilityof the attaching group.

A wide variety of compounds can be bonded through directcarbon-substrate linkages to substrates of the invention. A fewillustrative examples include carboxylic acids and their derivatives,generally represented as ##STR1## where, for example, G is --OH, --Cl,--H or --NR₂ (with R being an alkyl or hydrogen) and n is 0 to quitelarge, but typically 10 to 20.

Use of amides (where G=NHR) is particularly suitable for affinitychromatography applications. Additionally, nitriles and imines aresuitable, generally represented as CH₂ ═CH--(CH₂)_(n) --C═N and CH₂═CH--(CH₂)_(n) C═NR where R and n are as above described.

Turning to the figures, FIG. 1 illustrates a partial IR spectrum of ahydride intermediate embodiment prepared via a chlorination/reductionsequence according to the invention, as will be further described inExample 1. FIG. 2 illustrates a partial IR spectrum of another hydrideintermediate embodiment that was prepared via coupling of a poroussilica with triethoxysilane in accordance with the invention, asdescribed in Example 5. The spectrum of this material closely matchesthat of FIG. 1 which indicates that high conversion to the hydride ispossible by using this single step procedure. FIG. 3 illustrates apartial IR spectrum of an octyl-bonded silica embodiment preparedaccording to the invention, as described by Example 6. FIG. 4illustrates a partial IR spectrum of another octadecyl-bonded silicaembodiment prepared according to the invention, as described in Example7.

EXPERIMENTAL Materials and Methods

Toluene and diethyl ether (EM industries, Inc.) were dried by allowingthem to stand with calcium hydride (Sigma Chemical Co.) for severaldays, refluxing and then distilling from the hydride immediately beforeuse. A 0.2M lithium tetrahydridoaluminate (Sigma Chemical Co.) ethersolution was prepared and used as the reducing reagent. Thionyl chloride("gold label", Aldrich Chemical Co.) was used as received. IR qualitypotassium bromide (Harshaw/filtrol Partnership) powder was used for theFT-IR spectra. Partisil-40 (Whatman Inc., Clifton, NJ) with a 40 nm meanparticle size, 85 Å mean pore size and 350 m² /g surface area(manufacturer's typical data) was used as the silica material.

All silica derivatization reactions were carried out under a dry N₂atmosphere in glassware that had been previously dried at 120° C.overnight. The

LiAlH ether solution was prepared in a N₂ -flushed glovebag. Transfer ofliquids was carried out either with a glass syringe (<20 ml) or by meansof a stainless steel cannula and N₂ -pressure, via silicone rubbersepta. Prior to reaction, the silica was dried under vacuum at 120° C.overnight and then cooled in a vacuum desiccator.

Infrared spectra were taken in the 4000-450 cm. ¹ region with aPerkin-Elmer Model 1800 FT-IR spectrometer equipped with a Spectra-Techdiffused reflectance accessory. Dried ground KBr was mixed with an equalamount (by weight) of silica material. Samples were filled into theaccessory's cup by gently tapping until a small sample mound was formed.A very smooth sample surface was then obtained by pressing down amicroscope slide onto the cup while moving it in a circular motion.Before taking a spectrum, the height of the sample cup was adjusted byusing the alignment routine provided with the standard Perkin-Elmersoftware. This resulted in a reproducible positioning of the samplesurface at the optimum height so that a maximum signal throughput wasconsistently obtained. Spectra were collected at a nominal resolution of2 cm⁻³¹ 1 with a weak Norton-Beer apodization. 200 sample scans wereratioed against pure KBr as reference. Band intensities (absorbanceunits) for triplicate spectra of samples prepared in this manner hadrelative standard deviation equal or better than 7%. Spectra shown werenormalized to 100% transmittance.

ESCA measurements were done with a surface Science Laboratories modelSSX-01 spectrometer equipped with an Al Kα x-ray excitation source.Spectra were obtained at an energy resolution of about 1 eV from a600×1000 μm sample spot. Typically, the x-ray beam penetrated the top˜100Å of selected silica samples.

Example 1

5.00 g (approximately 14 moles of silanol, assuming 4.6 groups per nm²)of dried silica were suspended in 60 mL of freshly distilled, drytoluene, and 10.2 mL of thionyl chloride (about a 10-fold molar ratioexcess with respect to silanol content) were added. The mixture wasmagnetically agitated and the chlorination was allowed to proceed underreflux for at least 18 hours after which the excess SOCl₂ was distilledoff. Removal of any remaining SOCl₂ was carried out by washing thedark-purple product at least 8 times with 80-mL portions of dry toluenewhile magnetically stirring for 15 min. After each washing, and once thesolid had settled, the solvent was carefully aspirated off to waste bymeans of a vacuum applied to a glass pipette. Finally, the chlorinatedsilica was washed with one 30-mL portion of dry diethyl ether, remainingin a final fresh ether aliquot.

70 mL of 0.2M LiAlH₄ ether solution (about a 4-fold molar ratio,hydride: original silanol) were added slowly to the chlorinatedsilica/ether suspension. An immediate reaction was evidenced by a colorchange from dark purple to white. The reaction was allowed to proceedfor 2 hours under a gentle reflux. The excess of LiAlH₄ was aspiratedoff and destroyed by adding dry ethyl acetate (about 10 mL) followed byisopropanol dropwise with stirring until hydrogen evolution ceased. Thisalso confirmed that an excess of the reducing reagent was present at theend of the reduction reaction. The product was next washed as describedabove with eight 30 mL portions of dry ether to remove any remainingaluminum hydride and/or chloride species in solution. The "reducedsilica" was then dried overnight in a vacuum oven at 120° C.

EXAMPLE 2

The Si-H group is readily identified by a strong stretching band in therange 2300 to 2100 cm⁻¹, along with a relatively weak bending bandbetween 760 and 910 cm⁻¹, the former being located in a region where theabsorption due to the silica matrix is minimal. When chlorinated silicawas reduced with an excess of LiAlH, a broad peak was produced at about2280-2200 cm¹. The shape of the peak suggested a multiplet whoseposition is consistent with that of SiH species in which the siliconatom is bonded to several electronegative atoms. Although the multipletmay be attributed to more than one possible SiH species (namely --SiHand --Si(OH)H which originated from single and geminal silanolsrespectively), the formation of surface AlH (alane) species, which isalso feasible under the reaction conditions, may also explain at leastpartially the lowfrequency component of the broad absorption. Due to theexcess of reducing reagent, the presence of unreacted silanols and thevirtual absence of shielding effect from hydrogen atoms as the reductionof chlorinated silica progresses, the silanols become increasinglyaccessible to attack by the reducing reagent, believed to lead to theformation of surface alane species: ##STR2## This situation is contraryto that of most (if not all) silica derivatizations, in which theoriginal surface species become progressively unaccessible to themodifier's attack. Slow but unequivocal gas evolution (X - H in theabove reaction (1)) was observed after the reacting mixture was allowedto settle for several minutes and the reaction flask was gently tapped(in fact, gas evolution was more readily observed by using a much largerexcess of reducing reagent). This observation is further substantiatedby reacting a small amount of native (i.e., fully hydroxylated) silicawith ethereal LiAlH . A relatively broad and asymmetrical peak at 2181cm⁻¹, very likely due to surface alane species formed through reaction(1), was obtained.

EXAMPLE 3

To investigate the hydrolytic stability of silane as well as alanesurface species, small portions of reduced silica (chlorinated solidreacted with excess LiAlH₄) were treated with 0.01M NaOH, deionizedwater and 0.1M HCl. As evidenced from slow gas evolution and confirmedby IR spectra, treatment with aqueous alkali (pOH=2) resulted in thecomplete elimination of both alane as well as silane species while water(pOH=7) does so at a much slower rate. Acidic (pOH=13) treatment on theother hand resulted in the complete elimination of the low-frequencyalane component of the originally broad band and, interestingly, asignificant increase in the intensity of the 2260 cm⁻¹ Si-H band. Theobserved enhancement of the Si-H band intensity may be attributed to theeffect of either or both of two factors: (i) the hydrolytic removal ofIR active --Al--H species from the silica matrix which may cause anincrease of the effective penetration of IR radiation and thus a moreintense SiH absorption; and (ii) the formation of additional surface SiHspecies at the expense of adjacent alanes.

EXAMPLE 4

The ESCA technique can produce valuable information about manychemisorbed species present on the reduced silica surface, with theexception of hydrogen. Five consecutive 10-min. washings with aqueousHCl acid (10 mL of 0.5M solution per gram of solid) were carried out tothoroughly eliminated unwanted species present on the surface. Thisprocedure was found efficiently to remove chemisorbed aluminum(characterized by two peaks with binding energies of 75 and 116 eV) fromthe untreated material down to the background levels of unreactedsilica.

Curiously enough, traces of chemisorbed carbon (binding energy 281 eV)were also significantly found to be removed through acid treatment.Carbon chemisorption can be explained in terms of a secondary reaction(solvolysis) taking place during the reduction of chlorinated silica inethereal medium. Subsequent removal of the carbonaceous species duringacid treatment is consistent with the well known hydrolytic instabilityof the Si-0-C linkage.

Complete elimination of surface alanes from reduced silica is believednecessary in order to minimize the deactivation (via reduction) of ametal catalyst during the surface hydrosilation of terminal olefins.Treatment of the reduced material with aqueous acid should therefore beincorporated in the synthesis of the silica intermediate.

EXAMPLE 5

Five grams of silica (Partisil-40, 350 m² /g) were suspended in 125 mLof 0.1M HCl solution in 95% ethanol with magnetic stirring, and 3.5 mLof triethoxy silane (about 30% molar excess with respect to silanolcontent) were added. The reaction was allowed to proceed at roomtemperature for about 30 minutes after which the suspension wascentrifugated and the solid washed with five 50-mL portions of ethanol.The solid was filtered and finally dried at 110° C. under vacuumovernight.

The product obtained exhibited essentially identical spectroscopic,chemical and thermooxidative characteristics of that prepared viachlorination/ reduction sequence as described in Example 1. Thesimplicity and efficiency of this procedure make the hydridosilanecoupling a preferred method.

EXAMPLE 6

Five grams of hydride intermediate substrate (e.g., that prepared asdescribed by Example 1) are added to 60 mL of 1-octane (density 0.715g/cc, 90% purity) containing 75 μL of 0.lM chloroplatinic acid solutionin 2-propanol. The suspension was magnetically agitated and the reactionallowed to proceed for about 24 hours at 80±5° C. The mixture was thencentrifugated and the solid washed with three 40-mL portions of toluenefollowed by similar was ings with dichloromethane. The solid was thenfiltered and finally dried at 110° C. overnight. The octyl-bonded silicacontained 10.9% (by weight) of carbon, which corresponds to a surfacecoverage of about 3.7 μmole of octyl groups per square meter. The use ofan equivalent amount of the olefin-platinum complex dicyclopentadienylplatinum(II) dichloride as catalyst resulted essentially in the samelevel of surface coverage. A partial IR spectrum of the product is shownin FIG. 3.

EXAMPLE 7

Five grams of hydride intermediate material (e.g., that prepared asdescribed in Example 1) were suspended in about 60 mL of 1-octadecene(density 0.79 g/cc, 99% purity) containing 50 μL of a 0.2M solution ofdicyclopentadienyl platinum (II) dichloride in dichloromethane. Themixture is agitated and the reaction allowed to proceed for about 24hours at 90±5° C. after which the product is washed and dried asdescribed in Example 6. The octadecyl-bonded silica contained 11.8% ofcarbon representing a surface coverage of about 1.8 μmole of octadecylper square meter. This material represents another example of long-chainolefin hydrosilylation on a hydride-derivatized support. Similar resultsare obtained when chloroplatinic acid is used as catalyst. A partial IRspectrum of the product is shown in FIG. 4.

It is to be understood that while the invention has been described abovein conjunction with preferred specific embodiments, the description andexamples are intended to illustrate and not limit the scope of theinvention, which is defined by the scope of the appended claims.

It is claimed:
 1. A method for modifying the surface of an inorganicoxide substrate useful for chromatography or electrophoresis separationscomprising:converting surface hydroxyl groups of said substrate tointermediate surface hydride groups; and reacting said intermediatesurface hydride groups with an olefin reagent in the presence of acatalyst to form a reaction product thereof on the surface of thesubstrate, the reaction product having carbon atoms of the olefinreagent directly linked to the surface of the substrate.
 2. The methodof claim 1 wherein the converting is either by means of ahalogenation/reduction sequence or by means of a single silane couplingreaction.
 3. The method of claim 2, wherein said halogenation/reductionsequence comprises halogenation of the inorganic oxide substratefollowed by reduction of the halogenated material and then post-reactiontreatment with aqueous acid.
 4. The method of claim 3, wherein saidhalogenation comprises reaction with a chlorinating reagent.
 5. Themethod of claim 3, wherein said reduction comprises reaction of thehalogenated material with an inorganic hydride.
 6. The method of claim5, wherein said inorganic hydride includes aluminum hydrides or boronhydrides.
 7. The method of claim 2, wherein said silane couplingreaction comprises reaction of the inorganic oxide substrate with ahydrosilane coupling reagent of the formula H_(n) SiX_(4-n) where X is ahydrolyzable group, and n is an integer in the range of one and three.8. The method of claim 7, wherein said hydrosilane coupling reagentincludes triethoxysilane or trichlorosilane.